Injector flow rate on boosted application?

[Lennart]

After reading many posts on how to set up IFR I am curious as what to do when boost is applied?!
I am in the process of tuning a 2000 Sierra 5.3L with Whipple charger and #42 Delphi injectors. The fuel pressure regulator has a vacuum line hooked up to it.
Fuel pressure measured at the rail is 46-48psi at idle and 57psi when getting into 100+kPa MAP.
While still getting the bugs worked out and still waiting for the 2bar sensor to arrive it seems very difficult to get the desired AFR at boost to where I want it to.

[joecar]

The vacuum line to the FPR is the "MAP-reference".
The FPR regulates absolute fuel rail pressure to FP+BARO+MAP.
The absolute pressure inside the intake manifold is MAP.
The pressure difference across any one injector is FP+BARO+MAP - MAP which equals FP+BARO which is constant;
FP+BARO is a constant value regardless of MAP or vacuum (BARO-MAP)... i.e. regardless of boost or vacuum.
I don't know if the PCM modifies the IFR due to differences in BARO.

With engine running, remove the reference hose from the FPR to expose the FPR to barometric pressure BARO;
like this the FPR regulates to absolute pressure FP+BARO+BARO, which a pressure gauge measures as FP+BARO.
It would be good to see how FP+BARO varies under load/throttle/rpm...
if you have a good FPR and fuel pump, then the variation should be small
(the pump should provide more pressure than is needed, and the regulator should regulate it down to the fuel rail by bleeding off into the return line).

You calculate IFR = R0 * sqrt((FP+BARO) / P0)
where R0 is rated flowrate at rated pressure P0, and FP+BARO and P0 have the same units.

Remember to reconnect the reference hose.

Note: with reference hose connected, the regulated absolute rail pressure is FP+BARO+MAP which a guage measures as FP+MAP.

[Lennart]

Thanks for the info. I did read that in another thread but was wondering if the pressure regulator will also adjust for boost.

[joecar]

Yes, the MAP-referenced FPR adjusts rail pressure for boost/vacuum in a manner
which maintains constant pressure difference across any one injector.

This keeps each injector's IFR constant.

[eboggs_jkvl]

Is it a rising rate regulator? My fuel pressure regulator adds 1 PSI of fuel pressure for every 1 PSI of boost. I've a pressure line from the front of the MAF area that sends the boost signal back to the regulator. I run at 58 PSI normally and when I'm at 12.5 PSI of boost, my fuel pressure is 70.5 PSI. My A/F is 12.2 straight accross the run under boost. I'm running 60# injectors.

Elmer